Technical Field
This invention is in the field of proximity sensors and, in particular, a laser diode proximity sensor in a single integrated package.
Description of the Related Art
Proximity sensors are frequently used in cell phones, tablets, and personal computing devices. For example, when a person is making a phone call, a proximity sensor in the phone will detect when the phone is close to the ear or hair during a call to switch off the screen for touch sensitivity. Further, if the phone is placed face down on a surface, it will switch to screen off for power saving. The sensor may also include a ranging sensor to measure the distance to the object. In addition, the light sensor may include an ambient light sensor which is added to the proximity sensor or ranging sensor. The ambient light sensor in a smart phone will check the light in the immediate vicinity and vary the screen brightness to automatically adjust the screen based on the ambient light.
FIGS. 1A and 1B are images of a prior art proximity sensor 10. Looking at both figures together, the proximity sensor 10 of the prior art includes a plastic housing 12 which is glued with an adhesive 14 to a base substrate 16. Apertures 18 and 20 permit light to be emitted and received, respectively. The diode 22 emits light which will be sensed by the light sensor 24 if the proximity sensor is near an object, such as less than one to two centimeters away.
A glass lens 26 is attached by glue to the plastic cap 12 to protect the diode 22 and permit light to be emitted. Similarly, a glass lens 28 is glued to the plastic cap 12 adjacent the light sensor to protect and seal the cavity holding the chip and filter the light. The plastic cap 12 also includes a central barrier 30 which is adhered by glue to the chip 24 in order to block light passing directly from the diode 22 to the light sensor 28.
There are a number of shortcomings and difficulties with assembling the package of the prior art. A first difficulty is the number of small parts which must be assembled. The package has a footprint area in the range of 2.5 to 2.8 millimeters and therefore the individual components are very small. The automatic machinery that assembles the device has difficulty working with such small parts. There is also significant difficulty in lens placement accuracy. The lenses may tilt slightly, thus reflecting a large amount of light. The prior art has the disadvantage of a large chamber and light which may be reflected from the glass lens. Another problem is the glue dispensing process may create voids, bubbles, or bumps, which make the different parts uneven, including the plastic cap, the diode, the central barrier 30, and the lenses. Another problem is the likelihood of glue overflow. If too much glue is used, it may flow from underneath the central barrier 30 to cover part of the light sensing circuit 28. Accordingly, it is preferred to provide an improved proximity sensor.